Field of the Invention
The present invention relates to a method of ejecting air into a gas turbine casing to thereby prevent deformation in the turbine casing, a purging device for executing this method, and a gas turbine provided with this device.
Priority is claimed on Japanese Patent Application No. 2012-069085, filed Mar. 26, 2012, the contents of which are incorporated herein by reference.
Description of Related Art
A gas turbine is provided with; a compressor which compresses air to produce compressed air, a combustor which mixes fuel with the compressed air and combusts it to produce combustion gas, a rotor which is rotated by the combustion gas, and a casing which covers the rotor while allowing it to rotate therein. In this gas turbine, in a state where fuel supply to the combustor is stopped, high temperature gas is held within a turbine casing of the casing, and a temperature difference occurs between an upper part and a lower part of the turbine casing. As a result, a so-called cat back phenomenon occurs, in which the turbine casing upper part where the temperature is high expands relatively with respect to the turbine casing lower part where the temperature is low, deforming the turbine casing like the back of a cat.
If this cat back phenomenon occurs, spacing between the rotor and the stationary body partly becomes narrower, and there is a possibility that the rotor and the stationary body may come in contact with each other.
Consequently, in order to prevent this cat back phenomenon, Patent Document 1 cited below proposes a purging device which ejects air into the turbine casing. This purging device is provided with a first air ejecting pipe and a second air ejecting pipe for ejecting air into the turbine casing. The second air ejecting pipe ejects air inward from the outer side in the radial direction perpendicular to the rotor shaft. On the other hand, the first air ejecting pipe ejects air more toward the upstream side, that is, more toward the side toward the compressor side, with approach from the radially outer side to the radially inner side.